TMZ broke the story ... the former "Real World" star is threatening to sue HBO over the "Johnny's Bananas" storyline on "Entourage" -- claiming he owns the rights to the name, and never gave permission for the show to use it.

Johnny was out at Beso in L.A. last night ... and told us, "It's not like I spilled hot coffee on my vagina and I'm trying to make a buck off of it ... my identity has been stolen man."

He adds, "I've been on television for the last 5 years, acting like a jerk-off, creating this
name, making it a household name, and I'll be damned if some half-ass
gorilla is gonna come by and steal my thunder."